実験: SMTP ポートを叩いてみよう

まずは nslookup

% nslookup -type=MX *******.or.jp
  (略)
*******.or.jp     preference = 10, mail exchanger = ##1.*******.or.jp
*******.or.jp     preference = 10, mail exchanger = ##2.*******.or.jp
*******.or.jp     preference = 10, mail exchanger = ##3.*******.or.jp
  (略)

Stage 1

% telnet ##1.*******.or.jp smtp
Trying XXX.XXX.XXX.XXX...
Connected to ##1.*******.or.jp.
Escape character is '^]'.
220 ##1.*******.or.jp ESMTP server (○○×× vX.Y.Z ID# xx-yyyyy) ready Mon, 10 Feb 1997 22:43:54 +0900
QUIT
221 ##1.*******.or.jp ESMTP server closing connection
Connection closed by foreign host.

Stage 2

% telnet ##2.*******.or.jp smtp
Trying XXX.XXX.XXX.XXY...
Connected to ##2.*******.or.jp.
Escape character is '^]'.
220 ##2.*******.or.jp ESMTP server (○○×× vX.Y.Z evaluation license) ready Mon, 10 Feb 1997 23:10:25 +0900
QUIT
221 ##2.*******.or.jp ESMTP server closing connection
Connection closed by foreign host.

Stage 3

% telnet ##3.*******.or.jp smtp
Trying XXX.XXX.XXX.XXZ...
telnet: Unable to connect to remote host: Connection timed out